1. Field
The present invention relates generally to wireless power transfer, and more specifically to devices, systems, and methods related to adaptively tuning impedance in a receiver device to improve wireless power transfer.
2. Background
Typically, each battery powered device such as a wireless electronic device requires its own charger and power source, which is usually an alternating current (AC) power outlet. Such a wired configuration becomes unwieldy when many devices need charging.
Approaches are being developed that use over-the-air or wireless power transmission between a transmitter and a receiver coupled to the electronic device to be charged. Such approaches generally fall into two categories. One is based on the coupling of plane wave radiation (also called far-field radiation) between a transmit antenna and a receive antenna on the device to be charged. The receive antenna collects the radiated power and rectifies it for charging the battery. Antennas are generally of resonant length in order to improve the coupling efficiency. This approach suffers from the fact that the power coupling falls off quickly with distance between the antennas, so charging over reasonable distances (e.g., less than 1 to 2 meters) becomes difficult. Additionally, since the transmitting system radiates plane waves, unintentional radiation can interfere with other systems if not properly controlled through filtering.
Other approaches to wireless energy transmission techniques are based on inductive coupling between a transmit antenna embedded, for example, in a “charging” mat or surface and a receive antenna (plus a rectifying circuit) embedded in the electronic device to be charged. This approach has the disadvantage that the spacing between transmit and receive antennas must be very close (e.g., within millimeters). Though this approach does have the capability to simultaneously charge multiple devices in the same area, this area is typically very small and requires the user to accurately locate the devices to a specific area.
In addition to wireless energy transmission, electronic devices often use a number of different communication channels at various frequencies. Often, a device may need to include an antenna for each different frequency band, which can become expensive both in terms of space used on the device and cost of the various components to support the multiple antennas.
There is a need to reduce the number of antennas that may be required on a device for various functions, such as wireless power reception, near-field communication (NFC), and other communication functions that an electronic device may perform